Many research institutions are currently conducting research to develop Silicon Carbide (SiC) devices. Advantages of SiC power devices over traditional silicon devices include low on resistance, high switching speed, high temperature operation, etc.
Conventional silicon power devices, such as Insulated Gate Bipolar Transistors (IGBTs), are limited to about 150 degrees C. maximum operating temperature. Therefore, it is possible to employ Si devices even when using low melting point solder, such as a conventional Sn—Ag alloy based solder.
However, SiC based devices can theoretically operate to temperatures of 600 degrees C. If the SiC devices are employed at a high temperature when using conventional low melting point solder, they will lose their mechanical attachment to the circuit board due to the solder melting.
High temperature solders are currently being used to attach SiC, but they also present several problems. Manufacturing void free solder bonds is a labor intensive process that does not easily lend itself to mass production. The high processing temperatures necessary to employ high temperature solder joints can create thermal stress in the bond due to mismatches in thermal expansion between the substrate, solder, and SiC device. These thermal stresses can lead to premature failure of the circuits. Additionally, any material added between the device and the substrate increases the thermal resistance. For power devices that self-heat during operation, this can degrade the performance of the entire system.
Methods for creating an interconnect between the SiC devices and a low thermal resistance package have already been disclosed (for example, refer to Patent Literature 1 and Patent Literature 2). Patent Literature 1 and Patent Literature 2 disclose a fabrication method of a package used for housing a SiC device, and also disclose that the SiC device is bonded to other parts or conductive surfaces using Transient Liquid Phase (TLP) bonding technology.
Another disclosure details a solder compound whose melting point is comparatively low (e.g., the melting point is not more than 430 degrees C.) including Sn and/or Pb (for example, refer to Patent Literature 3). In Patent Literature 3, the solder alloy has a difference in temperature between the liquid phase and the solid phase smaller than that of the basic solder.
Another relevant disclosure details the transfer of metal MEMS packages using a wafer-level solder transfer technology (for example, refer to Non Patent Literature 1). In Non Patent Literature 1, a device wafer and a package cap are bonded by the TLP technology using relatively thin Ni—Sn layer.
A liquid cooling device for removing heat from a semiconductor element via a cooling device from the back side surface of the semiconductor element has been disclosed (for example, refer to Patent Literature 4).